The present invention relates to an ink jet printer, especially to an ink jet printer useful in multimode printing.
The requirements for an ink jet printer used for printing images, such as pictures and photographs, and for an ink jet printer used for text reproduction are quite different. In the former case the quality of the print is, provided that a minimum resolution is achieved, more determined by the absence of banding in even density parts and by the number of density levels printable per pixel than by the resolution. In the latter case, the image quality is more determined by the resolution and less by the absence of banding in even density parts and the number of density levels printable per pixel. This means that it is quite difficult to design a single printer that can print pages containing both imagesxe2x80x94e.g. photographsxe2x80x94 and text with high image quality.
In the art of ink jet printing, it is well known how to increase the resolution of a printer. E.g. in U.S. Pat. No. 4,922,271 a matrix printer, a.o. an ink jet printer, is disclosed having multiple printing heads positioned so as to enhance the resolution of the printer beyond the basic resolution of the individual printheads.
Also in U.S. Pat. No. 5,719,601 and U.S. Pat. No. 5,844,585 methods for enhancing the resolution in an ink jet printer beyond the basic resolution of the individual printheads are disclosed.
Also the problem of banding, especially in even density portions of an image, e.g. a picture or photograph, is well known and several measures to avoid this phenomenon have been disclosed; e.g. in U.S. Pat. No. 4,999,646 it is disclosed that by providing complementary and overlying swath patterns of ink jet print, and utilizing super pixeling in the overlying printed areas to generate dot-next-to-dot (DND) printed images, the uniformity and consistency of dot formation over the ink jet printed image could be enhanced. In various documents it is described to solve the problem of banding by printing a single line using more than one nozzle or by printing every dot with more than one nozzle, e.g. by printing half of the density needed with one nozzle and the other half with another nozzle. Also in U.S. Pat. No. 5,844,585 an enhanced form of shingling is disclosed. In U.S. Pat. No. 6,124,940 it is recognized that shingling demands a high data flow from the host computer to the printerxe2x80x94which requires a more expensive printing systemxe2x80x94and a method for diminishing the data flow is presented.
U.S. Pat. No. 6,234,605 discloses a liquid ink printer, depositing ink drops to form an image, in multiple printing resolutions, on a recording medium moving along a recording medium path. The liquid ink printer includes a pagewidth printbar, including an array of ink ejecting nozzles spaced at a predetermined resolution, aligned substantially perpendicular to the recording medium path, to eject the ink drops on the recording medium during movement of the recording medium along the recording medium path, a positioning device, coupled to the pagewidth printbar, to position the printbar at a plurality of discrete locations, and a controller, coupled to the printbar and to the positioning device, to cause the positioning device to position the printbar at the plurality of discrete locations as a function of the predetermined resolution.
Although the printers as disclosed in the referenced documents are well suited to have high resolution printing or low banding, there is still a need for a improved printer that can easily be tuned to the needs of the printing job at hand.
The present invention is an ink jet printer as claimed in the independent claims. Preferred embodiments of the invention are set out in the dependent claims.
FIG. 1 schematically shows an ink jet printer in accordance with the invention. The ink jet printer includes two nozzle arrays 101 and 101xe2x80x2, that may be maintained in a frame (not shown). The receiving substrate 103, upon which the image, the text or both are to be printed, is moved along a receiving substrate path in the direction of arrow A, the printing direction. In FIG. 1, the shown portion of the receiving substrate path is rectilinear. In general, the receiving substrate path may have other forms; the receiving substrate may e.g. be guided by a drum, the receiving substrate path may comprise a number of rectilinear portions and a number of curved portions, etc. The first and second nozzle arrays 101, 101xe2x80x2 are arranged one after another in the printing direction (i.e. either the receiving substrate first passes nozzle array 101xe2x80x2 and then nozzle array 101xe2x80x94as shown in FIG. 1xe2x80x94or it first passes nozzle array 101 and then nozzle array 101xe2x80x2xe2x80x94as shown in FIG. 2). Preferably, the first nozzle array 101 is positioned at a constant first ink-throwing distance from the receiving substrate path. Preferably, the second nozzle array 101xe2x80x2 is positioned at a constant second ink-throwing distance from the receiving substrate path, that may be different from the first ink-throwing distance. The first nozzle array 101 has a length L and a number N of nozzles 102 that are positioned in the array with a nozzle pitch NP; the second nozzle array 101xe2x80x2 has a length Lxe2x80x2 and a number Nxe2x80x2 of nozzles 102xe2x80x2 that are positioned in the array with a nozzle pitch NPxe2x80x2. The first nozzle array 101 is positioned so that its length L makes an angle xcex1 with the printing direction A, chosen so that 20xc2x0xe2x89xa6xcex1xe2x89xa6160xc2x0, and the second nozzle array 101xe2x80x2 is positioned so that its length Lxe2x80x2 makes an angle xcex1xe2x80x2 with the printing direction A, also chosen so that 20xc2x0xe2x89xa6xcex1xe2x80x2xe2x89xa6160xc2x0. In the embodiment shown in FIG. 1, the nozzle arrays 101, 101xe2x80x2 each have only one row of nozzles. In general, a nozzle array may comprise several rows of nozzles. The xe2x80x9clengthxe2x80x9d L, Lxe2x80x2 of a nozzle array is determined as the largest distance between the first and the last nozzle of a row of nozzles of the array (e.g. in case of an array consisting of 5 equidistant rows of 1000 equidistant nozzles, wherein the distance between the nozzles is NP and the distance between the rows is also NP, L=(1000xe2x88x921)*NP).
In the best mode of the invention, angle xcex1=xcex1xe2x80x2=90xc2x0 and the nozzle arrays 101, 101xe2x80x2 are xe2x80x9cpage wide printhead assembliesxe2x80x9d. A page wide printhead assembly is defined as follows. The receiving substrate has a width W (not shown in FIG. 1) orthogonal to the printing direction A, and a printable width WP (not shown in FIG. 1) that may be smaller than W in case there is at least one unprinted border. In a page wide printhead assembly, the number of nozzles N and the length L are so large that the printable width WP is covered, eliminating the need to shuttle the printhead assembly as is the case in shuttle printers. In a so-called shuttle printer, a printhead assembly has a length L that is substantially smaller than the printable width WP of the receiving substrate (or, in case the printhead assembly is at an angle xcex1 to the printing direction A that is different from 90xc2x0, L*sin xcex1 is substantially smaller than WP), so that the printhead has to scan the receiving substrate, i.e. to reciprocate, in order to cover the printable width WP.
A page wide printhead assembly can be obtained in different ways, e.g. by means of a single, xe2x80x9cmonolithicxe2x80x9d printhead, by means of a number of staggered printheads, etc.
In an ink jet printer according to the invention, the second nozzle array 101xe2x80x2 is arranged so as to be movable back and forth as indicated by arrow M. When moving the second nozzle array along the direction indicated by arrow M, the nozzles experience a displacement that has a non-zero component in a direction Mxe2x80x2 orthogonal to the printing direction A and a component (that is zero if xcex1=90xc2x0) in a direction Mxe2x80x3 parallel to the printing direction; this allows to change the mode, e.g. text or image mode, of the printer.
A first advantage of an ink jet printer in accordance with the invention is the availability of multimode printing: the user has the possibility to switch the printer in an easy way between two or, which is preferred, three of the following modes: pure image mode, pure text mode and mixed text/image mode.
Another advantage of the invention is that the amount of data that has to be sent to the printer may be minimized for each printing mode.
Yet another advantage is that the change-over from mode to mode can proceed during printing, i.e. without stopping the printer.
Further advantages and embodiments of the present invention will become apparent from the following description and drawings.